Phosphorus and nitrogen are synergistic in flame retardant finishes for cellulosic fibers; Tesoro et al, Textile Res. J. 38, 245-255 (1968). The use of N-hydroxymethyl dimethylphosphonopropionamide in conjunction with triazine is an example of a commerically successful finish based on this concept; Aenish Anslin et al, Textile Res. J. 39, 375-381 (1968). Thermochemical studies have indicated that if phosphorous and nitrogen atoms are directly linked, their flame retardant effectiveness might be enhanced; Barker, Textilveredlung 8, 180-186 (1974).
Among compounds in which P-N linkages are present, some have been claimed as flame retardant finishes; British 1, 126, 259. The performance of chloromethylphosphonic diamide as a flame retardant for cotton has been described; Morris et al, Textile Res. J. 43, 336-341 (1973), but the comparatively low degree of fixation and durability reported made this compound appear rather unattractive.
Excellent results have been reported in the treatment of cotton fabrics with bis-aziridinyl chloromethylphosphine oxide (BACPO); Textile Chemists and Colorists 6, 148-153 (1974). In the heat cure, and in subsequent launderings, the nitrogen content of BACPO is almost completely preserved. Its fixation to cotton can be attributed to the formation of an ether linkage with cellulose by opening of the aziridine ring and/or the ring-opening aziridine polymerization reaction.
Use of methylphosphonic diamide as a catalyst to improve the thermal carbonization of cellulosic fibrous substrates has been claimed, Moore et al, U.S. Pat. No. 3,527,564. Flame retardant use of MPDA is disclosed by Tesoro et al in the Feb. 1976, issue of Textile Research Journal.